Improved calibration method for refraction errors in multibeam bathymetries with a wider range of water depths

Abstract

Errors induced by inaccurate or insufficient sound speed profiles (SSPs) in the water column will cause refraction errors in multibeam bathymetries. Most existing methods focus on eliminating errors in shallow water. Thus, to address the problems in a wider range of water depths, a new method is developed. First, beams in each ping are divided into two parts with the nadir beam as a boundary, and beams in each part have one equivalent sound speed profile (ESSP). Then, the overlaps of adjacent swaths are used to estimate the gradients of ESSPs by minimizing the depth difference in the overlaps with the differential evolution (DE) algorithm. To verify the proposed method, two datasets, i.e., one with artificially introduced refraction errors from water depths within 24 m and the other with refraction errors from water depths within 300 m, are calibrated. The results show that the mean and standard deviation (SD) of the depth difference between the results of the proposed method and the in situ measurements in the shallow water data are approximately -0.006 m and 0.006 m, respectively. The mean and SD of the depth difference between the results of the proposed method and the in situ measurements in the deeper water data are approximately less than -0.066 m and 0.266 m, respectively.